There is a switching power supply configured to generate a predetermined voltage and current using, for example, a switching element as a power supply configured to illuminate an illumination light source. In such a switching power supply, a high-frequency current is generated by switching the switching element intermittently between ON and OFF. Therefore, Electro Magnetic Interference (EMI) caused by a switching noise is generated, and hence a noise enters an input line and an output line. Since a switching frequency is increased in association with high-efficiency and reduction in size, the influence of the EMI is also increased.